Talk about eyes rolling into the back of their heads... hehe
The problem with rumorsville type of environments is that if you don't set the record straight yourself, then you'll likely have kidney stones, brain cancer, and only have 3 months to live by the time you get back.. In environments like that, the rumor will escalate in lieu of having the facts.
I worked in such an environment when I was diagnosed. When asked, I bluntly answered. Those that cared enough to ask for more details, I spared none. Those that didn't, I didn't bother forcing it on them. By the time surgery time was upon me, probably 20% of the office knew what was really going on.. I was visited in the hospital by several co-workers, at home by another few (even went to lunch with one while I was recovering), and to my suprise even one of the owners of the company came to visit me at home to check on me (truth be told, we're similar ages with kids roughly the same age and many of the same hobies...i.e. we're very much alike and get along great).
I certainly undertand the need to keep it private to avoid the rumor mill, however what you need to realize is that the true rumor mill will go on and fill in the blanks and with something that you may not like. For many, that won't bother them. For others, that would. It's all about what's more comfortable for you and your work environment.
Regards,
Brian